Pinewood Derby Times Volume 5, Issue 6

I overheard a conversation the other day, between two young men (young from my perspective). One of them said, “My car is pulling to the left, and I have to constantly adjust to keep it going straight. I think something is seriously wrong, but the shop says I just need an alignment. An alignment!? I paid a lot of money for the car; it shouldn’t need to be aligned? It’s supposed to be a precision car!”

Maybe this is a common misconception of younger drivers. I have driven a number of older cars, and alignment adjustments were needed on a regular basis. Newer cars seem to have fewer alignment issues, but it is still a recommended maintenance procedure. Why is that?

All cars (regardless of price or quality) are designed with the ability to make adjustments to the alignment. Why? When the car was originally assembled, the alignment was set properly. But over time, rough roads, tire wear, and generally wear and tear of the steering components affect the alignment. If the alignment is not adjusted regularly, excessive stress is placed on the steering components, and the tires wear unevenly (and more quickly).

How does this relate to pinewood derby cars? In an automobile, a minor alignment issue can be readily corrected by the driver, so the car goes straight. But with a pinewood derby car, the only ‘driver’ is the guide rail(s). Thus, any alignment issue will result in excessive collisions with the guide rail. Since every collision reduces the speed of the car, the desire is to minimize or eliminate guide rail collision. How? By setting the alignment to be as accurate as possible.

These products (and others) will minimize the amount of alignment needed. But just like an automobile, regardless of the level of precision or cost, wheel alignment is still necessary.

TEST TRACK In order to adjust the alignment of a car, you must first have a way to measure the amount and type of misalignment. I have found that this is most readily accomplished with a test track. Don’t let the words ‘test track’ scare you. This is simply a hard, flat, pitched surface, down which the car is rolled. In Volume 3, Issue 13 (March 17, 2004) there are plans for a nice test track. But here is a simple solution:

Get a sheet of MDF (medium density fiberboard) which is a material available at any home store. Have the store cut off a piece 8 feet long by 2 feet wide (you might be able to buy a piece already cut for shelving).

Down the very center of the board, draw a straight line with a permanent marker.

Lay the board on a flat surface. Test the surface first with a level, and orient the board so that it is running in the downhill direction (patios, garages, driveways, etc.

Prop up one end of the board about 4 inches, and place a pillow at the low end.

Use a ‘level’ to make sure the board is level at all points. Use small pieces of wood or other material (I use business cards) to shim the board as needed.

To test the car, place it at the uphill end and align the edge of the car with the straight line drawn on the board. Make sure to place it the same way on each test – a slight difference in placement will make a big difference in the measurement. After you are satisfied with the placement release the car and observe the direction and amount of drift. The goal is to get the car to deviate less than ½ inch over the 8 foot run. Test the car a few times until you have a good idea of the amount and direction of drift.

ALIGNMENT PROCEDURES There are two primary methods for adjusting wheel alignment: the axle bend method, and the axle shimming method. A third method (if the car has axle slots), angling the axles, is not recommended as it can cause binding between the axle and wheel bore.

Axle Bend Method

The axle bend method is cruder than the shim method, but is the method of choice if time is short. It is most easily done on a car with a raised front wheel. The method is quite simple:

Remove the front wheel/axle which is on the ground,

Make a ‘slight’ bend in the axle, and then reinstall the wheel/axle (see Figure 1),

Test roll the car, and then slightly rotate the axle by grasping the head of the axle with a pair of pliers,

Repeat until the car goes straight, then make sure to glue the axle in place.

Figure 1 Axle Bend Method

Wheel Shimming Method

The axle bend method corrects alignment by imparting some toe-in, toe-out, or some cant. Although it works, there is some energy loss in the front wheel due to this correction. A better way is to set all four axles such that each is parallel to the ground (no cant), and pointed in the same direction (no toe-in or out). This can be accomplished by placing thin (2 to 3 thousandths inch thick) shims between the axles and the car body such that the desired alignment is accomplished. The shim method was developed by Stan Pope, and is documented both on his web site, and in our booklet Speed to the Finish. Due to the length of the procedure, I won’t include it in this article, but here are some considerations.

To fully implement the method is somewhat tedious and time consuming. Plan on several hours to complete the process.

If you don’t have the time (or patience) for the full procedure, you can apply the method to the front wheels alone (or to the front ‘steering’ wheel if one front wheel is lifted). In this case, the shim method generally gives better results than the axle bend method.

FINAL THOUGHTS Wheel alignment is a critical procedure for ensuring top speed. Whichever method you choose to implement, make sure to allocate time for alignment. Then as long as the car is accurately placed on the track (see the tip below), whatever time you spend aligning the car will pay off at the track.

Pinewood Derby MemoryThe Wrong Lube

Last year was a poor year for pinewood derby performance for my sons. From the scout store we had purchased the pinewood derby speed kit that included: sandpaper, extra nails, a white powder (that I thought was Teflon lube), wheel mandrel, etc. Then we went to work.

The cars were the boy’s designs. One was a limo, and the other a cross between a submarine and a shark. We used a drill press to get straight axle holes, then we sanded the wheels and nails. We painted the cars, and even bought two plastic models to get decals to use on our cars. We then lubricated with the white powder. The wheels just didn’t spin for very long, but we were in the middle of a move so I couldn’t put any more time into the cars.

Our cars performed marginally well – we won a few heats and lost a few heats. But they were a lot slower than our prior year cars. My boys were disappointed in not winning as many heats as in previous years.

After the race when we had more time I decided to find out what was wrong. Oh, you probably know already. The white powder wasn’t lubricant, but instead it was axle polish (powdered pumice). When I cleaned out the powder and replaced it with graphite, the wheels spun like crazy. We learned how to really polish axles, and what not to use as a lubricant on race day!

Michael Law

Q&A

When I polish the axles, should I polish them in the direction the wheels will spin on the axle?

I don’t believe it makes any difference. Once the axles are polished, there should be no trace of any lines on the shaft, so the spin direction shouldn’t matter.

Our district has decided to allow extended wheel base this year. What are your recommendations for axle positioning from the front and rear of car?

On extended wheelbase cars, we set the axle holes at just a little over 5/8 inch from the ends of block. This allows the front wheels to stay just behind the front of the car. However, some people set the rear wheels at 5/8 inch, but the front wheels at 3/4 inch (or so). This ensures that if the car body is shortened due to excessive sanding, the front wheels will still not extend beyond the front of the car.

What is the best way to lubricate the axles with graphite?

Before installing the wheels/axles, place graphite in the hub of the wheel, insert the axle, then spin the wheel on the axle about 10 times. Then with the wheel hanging downward, place graphite in the wheel bore area, tap the wheel gently to shake the graphite into the bore, then spin 10 more times. Finally, repeat the previous step.

Want Answers? Do you have a pinewood derby-related question? If so, e-mail us your question.We answer all questions by e-mail, but not every question will appear in the Q&A section of the newsletter.

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